1. Technical Field
The present invention relates to a power steering apparatus structured such as to drive an actuator for assisting a steering in correspondence to an operation of a steering member such as a steering wheel or the like, and assist the steering on the basis of a generating force of the actuator.
2. Description of Related Art
As a power steering apparatus for a motor vehicle, there has been generalized a motor-driven power steering apparatus provided with an electric motor as an actuator for assisting a steering. The motor-driven power steering apparatus is structured such as to detect a steering torque applied to a steering member such as a steering wheel or the like by a torque sensor arranged in the middle of a steering shaft coupling the steering member and a steering mechanism, determine a target assisting force on the basis of a direction and a magnitude of the detected steering torque, and control so as to drive a motor for assisting the steering for generating the target assisting force (for example, refer to Japanese Patent Application Laid-Open No. 2004-338562).
Further, in recent years, even in a hydraulic power steering apparatus provided with a reciprocating type hydraulic cylinder (power cylinder) arranged in the steering mechanism as the actuator for assisting the steering, there has been proposed a hydraulic power steering apparatus structured such as to detect a steering torque applied to the steering member by a torque sensor, control a hydraulic control valve supplying and discharging a operating fluid to and from the power cylinder on the basis of the result of detection, and correspond to a change of an assisting force characteristic in correspondence to a traveling state such as a vehicle speed, a yaw rate and the like (for example, refer to Japanese Patent Application Laid-Open No. 11-180332).
The torque sensor used in the power steering apparatus as mentioned above is generally structured such as to divide the steering shaft forming a detected subject into a first shaft in a side of the steering member and a second shaft in a side of the steering mechanism, coaxially couple them by a torsion bar having a small diameter, and detect the steering torque applied to the steering shaft on the basis of the operation of the steering member via a relative angular displacement generated between the first and second shafts in connection with a torsion of a torsion bar.